WebGPURenderer: Add individual dispose for CanvasTarget caching

[sunag]

Related issue: #32690

Description

Allow CanvasTarget to remove cache dependencies individually after canvasTarget.dispose().

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	359.57 85.37	359.57 85.37	+0 B +0 B
WebGPU	629.79 174.92	629.85 174.95	+59 B +33 B
WebGPU Nodes	628.37 174.67	628.43 174.7	+59 B +32 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	491.31 119.78	491.31 119.78	+0 B +0 B
WebGPU	703.41 189.92	703.47 189.95	+59 B +32 B
WebGPU Nodes	652.61 177.31	652.67 177.34	+59 B +32 B